Preinsulated electrical connectors having recoverable sleeves are commonly used for splicing and terminating electrical wires. The connector is comprised of a wire connecting means, such as a solder ring or crimpable wire barrel positioned inside of a heat recoverable sleeve. Electrical connection is effected by inserting the stripped ends of the wire into the wire connecting means and fusing the solder ring or crimping the barrel around the wire. The ends of such a sleeve generally extend beyond the wire connecting means and over the insulated portion of the wire. Upon applying a sufficient amount of heat to the sleeve, the sleeve recovers radially in an encircling relationship around the wire connecting means and around the wire which extends from the ends of the sleeve.
In order to ensure a better seal between the end of the sleeve and the wire which extends from the sleeve, fusible inserts are positioned inside the ends of the sleeve which are to receive wires. As the sleeve is heated, the fusible inserts soften and conform closely to the wire, thus sealing the gaps between the sleeve and the insulation on the wire. U.S. Pat. Nos. 3,243,211; 3,312,772; 3,396,460; and 3,708,611 disclose splice connectors which use insert rings to increase the seal between the sleeve and the wire. The inserts of the instant invention are distinguished from those of the prior art by being fusible yet not truly liquid when melted. This precludes their being extruded from their desired location during the establishment of the connection and sealing thereof. In explanation, the sealants of this invention have a melt viscosity of 3,000 to 11,000 poises at 400.degree.-450.degree. F. (204.degree.-232.degree. C.). This is 300,000 to 1,100,000 times the viscosity of water. In short, instead of behaving as a fluid, the molten sealants resemble sticky gums which are readily deformable and conform and adapt to the local topography of the wire jacket surface.
In recent years there has been an increased demand, particularly in the aircraft industry, for preinsulated connectors that remain stable even when the connectors are subjected to high operating temperatures, 356.degree.-374.degree. F. (180.degree.-190.degree. C.). In addition, the connectors must be environmentally sealed and impervious to corrosive chemicals such as jet fuel and lubricants. For many applications, the connectors must also be flame retardant.
Sealing materials known in the art, such as polyolefins, polyamides and polyesters, are generally not satisfactory under the above described conditions. Many of these materials have melting points that are lower than the operating temperature of the equipment in which the connectors are used. The sealant, therefore, flows from the ends of the recovered sleeve and exposes the wire connecting means to environmental attack. Others of these known sealants are attacked by the corrosive chemicals and deteriorate, thus exposing the spliced wires. Furthermore, wires used in high temperature applications generally are insulated with tetrafluoroethylene. Sealants such as those listed above do not adhere well to this insulation. Additionally, these sealants are not sufficiently flame retardant.
Use of the sealant composition as disclosed herein eliminates the aforementioned problems. The sealant is both stable at elevated temperatures and essentially chemically inert to common solvents, jet fuels, and lubricants. It also adheres to wires having tetrafluoroethylene insulation. Furthermore, it is flame retardant.
The sealant is a homogeneous mixture comprised of about 64% to about 93% by weight of polyvinylidene fluoride (hereinafter referred to as PVDF), about 3% to about 32% by weight of a methalcrylate polymer and approximately 4% antimony oxide. In the preferred embodiment, approximately 4% zinc oxide is added to the mixture to increase the stability of the sealant mixture during the manufacturing processes.
Fusible sealant inserts are made by cutting sections from a tube extruded from the mixture, the outside diameter of the tube being dimensioned to fit inside the heat recoverable sleeve.
The use of the sealed inserts can be understood by referring to the following drawings.